It was the little pharmacy just before the last 7-11, going up Suthep Rd..  There was a very competent female, who speaks excellent English.  Turns out, she was an honor graduate at CMU.  Now, they've moved a few doors down (by the bakery), to a larger place, extended the hours, and added another English speaking pharmacist, who just completed a 6 year program at CMU.  He works days; she work evenings until Midnight.  They cater mostly to CMU students, and they have about the lowest or equal to lowest prices on anything that I've purchased.  I'm sure there are some things they don't have, but they would be glad to point you in the right direction, and there are many pharmacies on Suthep.  No steroids, no Tramadol......My only interest in the place is that I am lucky to have two very knowledgeable pharmacists near my home.  Support a viable, competent business, that likes to help farang.

There is also a very good one at the end of Chang Klan Rd , before the Rati Lanna hotel on the right hand side.

3 pharmacists and all speak very good English for the ones that live on the other side of town.